Both phenol and cyclohexanone can be produced from cyclohexylbenzene. For example, cyclohexylbenzene is oxidized to cyclohexylbenzene hydroperoxide, and the latter then subsequently cleaved to produce phenol and cyclohexanone. In a typical reaction, the cyclohexylbenzene conversion in the oxidation step is in the range of about 15 to 25 weight percent, which helps to minimize side reactions while maintaining high selectivity to cyclohexylbenzene hydroperoxide. It is not feasible, though, to remove cyclohexylbenzene hydroperoxide from the reaction product stream because of its chemical reactivity and thermal instability. Thus, the cyclohexylbenzene hydroperoxide must be cleaved to phenol and cyclohexanone before separations are attempted.
The resulting admixture of cyclohexylbenzene, phenol, and cyclohexanone, however, is difficult to separate even by distillation techniques because phenol and cyclohexanone form a maximum boiling azeotrope of about 72:28 weight percent boiling at about 184.degree. C. at substantially atmospheric pressure, and therefore cannot suitably be separated by fractionation. In addition, cyclohexylbenzene appreciably codistills with the azeotrope, resulting in additional separation problems.
To make the production scheme of cyclohexylbenzene to phenol and cyclohexanone viable, methods must be found to adequately separate out the cyclohexylbenzene for recycle.